Saw this last night, and I feel the replies thus far have a pretty good read on the whole thing. This feels like the kind of movie a computer would make if you told it to try to win an Oscar: it inserts various heartstring-tugging elements, but misses out on the fact that it is not the elements themselves, but the point they come together to make, that helps a film resonate. None of the performances really stood out, Asa Butterfield was so-so, and the whole thing lacked a point.
The ending was so frustrating, though not for the obvious reasons. All I could think as it all came together was "what?! If this movie had these kinds of" -- forgive the expression -- "balls, where were they for the other 98% of the film?" It's horrible, of course, but it's also interesting, inventive, and gutsy. In other words, it's everything that the rest of the film wasn't.
Whenever I see such a dramatic ending, I usually find that I can run back through the film in my head and see various foreshadowings, and all sorts of new thematic meaning is fed into what's come before. In this case, it was just an event. It didn't flesh out or resolve anything. It just happened. I think you guys hit the nail on the head when you talk about Thewlis' reaction. The reaction was all we got; there was no overarching moral, no hard lesson learned, no nothing. It just happens, and then it's over. What a waste.
There is just one exception: there is a nice little parallel (intentional or not) between Thewlis' interrogation and punishment of Karl and his father's disloyalty, and his own son's demise. Bruno clearly, by film's end, has come to disagree with the party line. Fate itself prosecutes Bruno using his Father's own standards. Then again, this bitter irony is undermined by a) the fact that they make some similar points in the subplot with his mother's dissent and demise, and b) the fact that the movie isn't really about him for the most part.
Speaking of Thewlis' mother, I assume we're supposed to believe that she was carted off or killed by the Nazi Party? It seems so obvious that I feel silly even asking, but I figure it can't hurt.
Random divergence: the character of Karl was a joke. They're already Nazis...does the story gain anything by having one of them suddenly scream all the time? And would he really shriek at and talk down to the child of his commanding officer so readily? I thought the whole thing was a bit over the top. I have no problem with one of the officers there being strangely sadistic or cruel, but it came across as almost comical.
That leads me right into the next point: I can't agree more with the sentiment that the film's moves were telegraphed. Hearing that Thewlis' mother is "ill," seeing the smoke in the distance, and as shocking as the ending is in a vacuum, it's perfectly obvious what will happen the very moment that Bruno offers to crawl under the fence. Given how shocking the ending is meant to be, I think a much shorter duration of time between this decision and the film's conclusion would have been wise. When it takes ten minutes, we have plenty of time to realize where it all has to go, and to steel ourselves for it. If it actually took place just a minute or two after, the shock might be more pronounced. Of course, that may have been deliberate: the filmmakers may have felt that the turn of events was disturbing enough that people needed time to realize it was going to happen.
Anyway, as I said earlier, the ending bugs me, because it opens up lots of possibilities that never come together. I think you could easily go back and sprinkle in a few details, and use the ending as a way to reveal that the entire film was about the Father, or something of the sort. As it is it's not much more informative or complicated than a documentary about any child who is part of a horrible accident.
If there is any kind of theme or moral or message at all, I suppose it's simply that there are certain truths that are plainly obvious to the youngest or simplest of us, and that mistakes on a certain scale can only be made by more informed, intelligent people, smart enough to rationalize them away. I rather like the implication that even simplistic questions from a child about the Nazi philosophy is enough to reveal its ignorance, but the idea that children see certain moral issues with more clarity than adults is hardly revelatory enough to necessitate an entire film.
By the by, I notice via IMDB that Thewlis' character is merely named "Father." I don't think we even get so much as a last name. Given that the film goes well out of its way to use the term "Fatherland" a good half-dozen times, perhaps there's some overt symbolism in the book that may have been lost in the translation, something about the Father as a metaphor for all of Germany.